In conventional manner, fan blades made out of composite material, in particular out of carbon fibers, are made from a stack of pre-impregnated unidirectional plies that are placed in a mold with the successive plies having different orientations, prior to compacting and polymerizing in an autoclave. That technique is very difficult and requires ply-stacking operations to be performed manually, which is lengthy and expensive.
Proposals have also been made to prepare woven preforms of dry fibers that are subsequently assembled together by stitching, prior to being impregnated by injecting resin into a closed mold. An alternative has consisted in making a single woven preform that is assembled together with one or more solid inserts prior to injection. Those solutions (patent documents U.S. Pat. Nos. 5,672,417 and 5,013,216) nevertheless present the drawbacks of requiring a plurality of parts to be assembled together and of creating within such assembly zones sites that are particularly likely to be weak, e.g. as a result of delamination, which is very harmful in terms of mechanical strength, in particular for ability to withstand impacts.
In order to overcome those drawbacks, patent document FR 2 861 143 proposes making a preform out of three-dimensionally woven yarns or fibers making it possible on its own, possibly after being cut out and having a binder injected therein, to form the final part forming all the portions of the turbine engine blade, without having recourse to inserts or any other fitted element.
In particular, use is made of the fabrication method described in patent document FR 2 892 339, during which the woven and then cut-out preform is put into place in a mold prior to injecting the binder and then proceeding its hardening.
Nevertheless, at present, various problems remain associated with the way in which the shaping is implemented.